This project provides continued morphologic support for the identification and classification of microsporidia isolated in tissue culture and inoculated into rhesus monkeys for development of an animal model. Morphologic characterization of Encephalitozoon hellem, a new microsporidian parasite isolated from the eyes of AIDS patients, has been introduced into SIV-infected monkeys. Lesions are seen predominantly in the liver and kidney and are characterized by acute multifocal necrosis of liver, necrosis of renal tubules and colonization of renal epithelium. Similar lesions are demonstrated in SIV-infected monkeys inoculated with E. cuniculi and E. intestinalis. The rhesus monkey represents a significant animal model for microsporidial infection since E. hellem and E. intestinalis a re only found naturally in humans (except for one report of EH in parakeets). E. bienusi, the most frequently reported microsporidial infection in humans, has been reported as a natural infection in at least one monkey colony (NERPRC) but natural infections have not been detected at TRPRC.